1. Field of the Invention
The present invention relates to methods and devices for the treatment of spinal stenosis.
2. Description of the Related Art
Spinal stenosis is a condition in which the spinal canal is narrowed, resulting in compression of the spinal cord and corresponding nerves. Possible causes of spinal stenosis include osteoarthritis, degenerative disc disease and other conditions associated with aging. Many people suffering from spinal stenosis often have spinous processes of adjacent vertebra that are abnormally close. Pressure on the spinal cord may be reduced by implanting a device that separates the spinous processes.
World Intellectual Property Organization (WIPO) Publication WO 2005/009300 describes a prosthesis inserted between spinous processes to prevent back pain. The prosthesis is comprised of an elastic material and includes a rigid central rod extended along its horizontal axis. The elastic material prevents leakage of liquids and gases and may be composed of rubber or silicon. Additionally, the prosthesis may have a dumbbell shape and may include expandable pockets within end sections and within a central section of the prosthesis. Prior to implantation, the pockets are filled with a substance, such as ethyl ether, that expands when exposed to body heat. The end sections are positioned along the sides of the spinous processes and the central section is positioned between the spinous processes.
WIPO Publication 2007/110604 discloses an expandable spacer including a flexible enclosure and a central tubular section extending along the horizontal axis of the enclosure. The flexible enclosure includes two end sections and a central section that may adapt to the shape of spinous processes when inserted between them. Further, the length of the central tubular section may be adjusted to stretch the flexible member so as to reduce the cross-sectional area of the spacer during insertion. After the spacer is inserted between spinous processes, the length of the central tubular section is reduced and the flexible enclosure is injected with a settable polymer resin through the central tubular section. Subsequent to polymerization, the end sections of the flexible enclosure retain the spacer in place and the pressure of the central section may control the separation between the spinous processes.
U.S. Pat. No. 5,549,679 discloses methods for treating spinal degeneration by inserting an expandable implant between vertebral bodies. The method may begin by boring out a portion of a degenerated disc and portions of neighboring vertebral bodies. Thereafter, the implant is inserted within the bored cavity and a bone graft material is injected within the implant. The implant is elliptical in shape and is porous, thereby enabling ingress and egress of fluids to permit growth of blood vessels, fibrous tissue and bone through the implant. The implant is sealed after it has been filled with the material. The patent also states that the filled implant may alternatively be positioned against the exterior lamina bone of adjacent vertebra to promote bone grafting of adjacent vertebra.
U.S. Pat. No. 7,226,481 and related U.S. Publication No. 2006/0149379 disclose methods for treating several spinal abnormalities including compression fractures by employing an implant similar to the patent described in U.S. Pat. No. 5,549,679. The references further describe inserting the implant within the vertebral body between vertebral end plates to displace diseased or damaged tissue or bone when filled with bone graft material.